Deformable chromium steel



1965 J. THOMPSON ETAL 3,222,163

DEFORMABLE CHROMIUM STEEL Filed April 12, 1963 UNIFORMLY DEFORMABLE ROP'NG mo NON-ROPING CHROMlUM,7o

CARBON,%

INVENTORS JAMES THOMPSON JOHN L. LAMONT JOHN W.FARRELL A TTORNEY United States Patent 1 3,222,163 DEFORMABLE CHROMIUM STEEL James Thompson, Niagara Falls, John W. Farrell, North Tonawanda, and John L. Lamont, Niagara Falls, N.Y.,

assignors to Union Carbide Corporation, a corporation of New York Filed Apr. 12, 1963, Ser. No. 272,620 2 Claims. (Cl. 75--126) This application is a continuation-in-part of our copending application Serial No. 149,005, filed October 31, 1961, now abandoned.

The present invention relates to chromium steels. More particularly, the present invention relates to a uniformly deformable chromium steel and to cold-formed articles manufactured therefrom, which articles are in all instances free from the surface defect known generally as roping.

Stainless steels containing upwards of 12 percent chromium, such as Type 430 (American Iron and Steel Institute classification) ,have been heretofore employed in the cold forming of such articles as cooking utensils, automotive trim, and equipment used in the food processing and chemical industries. However, in the many instances where final appearance is important, the frequency of the occurence of small ropelike ridges at the surface of the cold-formed articles has required a substantial amount of abrasive polishing and bufiing to provide a satisfactory finish. Due to the necessity of additional treatment after cold-forming, a substantial econornic penalty is placed upon the use of chromium steels in applications of the type described.

The aforementioned problem of roping in chromium steels is of long standing and repeated efforts have been made to provide a solution. One type of approach has been to employ-particular combinations of mechanical working and heat treating operations to commercially available chromium steels as disclosed in U.S.Patents 2,772,992 to Kiefer et al and 2,808,353 to Leffingwell et al.

Another technique, as described in US. Patent 2,851,384 to Waxweiler, is to critically control both the composition and heat treatment of chromium steel to secure a desired ductility by phase transformation in the steel.

While technically effective, these methods have substantially increased the cost of the chromium steel and hence have not provided an entirely satisfactory solution to the problem.

A still further effort to solve the problem of roping involves the addition of alloying elements to chromium steels. While this technique, particularly the use of columbium as disclosed by Becket and Franks in US. Patent 1,954,344, reduces the roping phenomena, the added expense of providing the additional alloying elements offsets, to a significant extent, the advantage gained by their use.

It is therefore an object of the present invention to provide a chromium steel which is uniformly deformable under strain.

It is another object to provide a chromium steel which is amenable to cold-forming into articles which are free from roping.

It is another object to provide a uniformly deformable, non-roping chromium steel which does not require additional alloying metals in order to ensure its deformable and non-roping characteristics.

It is another object to provide a uniformly deformable, non-roping chromium steel without requiring special heat-treatment of the steel.

Other objects will be apparent from the following description and claims taken in conjunction with the drawing in which:

The figure of the drawing shows a curve defining the proportions of chromium to carbon which are required in the chromium steel of the present invention.

3,222,163 Patented Dec. 7, 1955 The novel steel of the present invention is a ferritic, chromium bearing steel containing from 12 to 26 percent chromium, a maximum of 1 percent magnanese, a maximum of 1 percent silicon and up to about 0.18 percent carbon, the actual carbon content being restricted to amounts to the right of the curve in the accompanying diagram, the balance being substantially all iron and incidental impurities. Nickel and nitrogen are not essential in the composition of the present invention but may be present in amounts up to a maximum of 0.4 percent and 0.04 percent respectively. Higher values of nickel and nitrogen are avoided in the present invention in order to provide an essentially nontransformable ferritic steel which can be cold-worked into rope-free articles without the necessity of special heat treatment.

The chromium steel of the above composition is characterized by being uniformly deformable under strain and by the capability of being cold-formed by folding, flanging, deep drawing or spinning into articles which are free from roping. Additionally, microscopic examinations of cold-formed steels of the present invention have shown a fine, highly uniform grain structure consisting of ferrite and highly dispersed carbides.

The novel chromium steel of the present invention can be produced and processed in the same manner as other chromium steels with no special mechanical or heat treatments being required. For example, the ferritic steel of the present invention can be processed in the manner described and illustrated in The Making, Shaping and Treating of Steel, seventh edition, at pp. 859 et seq.

While the precise theory by which the advantages of the present invention are obtained is not known, it is believed that these advantages are due primarily to the formation of carbides and the ultimate uniform distribution thereof in the steel which is made possible by critical compositional control. The most important and critical compositional relationship in the steel of the present invention is that which is maintained between carbon and chromium as illustrated in FIGURE 1. Also, as previously mentioned, the nickel and nitrogen contents should not exceed 0.4 and 0.04 percent respectively.

With reference to the figure of the drawing, the steels of the present invention require that the carbon content, for a specific chromium content, be restricted to corresponding values to the right of the curve set forth in the drawing.

A particularly advantageous chromium steel in accordance with the present invention contains between 17 and 26 percent chromium and between about 0.1 and 0.17 percent carbon. The steels defined by this compositional range have nearly the same mechanical properties and, in cold worked form, are characterized by extremely high, quality, rope-free surfaces.

Various tests and studies of the compositions of the present invention have shown that when these steels are processed by the conventional techniques used for plain chromium steels, the articles obtained are uniformly deformable and, when in the form of sheets, strip and the like, can be directly cold worked to produce rope-free articles such as automobile hub-caps, head light rims, snap trim, window trim, sinks, counter-tops, plumbing fixtures, hospital ware and the like.

This capability demonstrates that special heat treatments and phase transformation are in no way required in producing the chromium steel of the present invention and that the benefits derived therefrom are due to critical control of the carbon-chromium proportions of the steel.

The following example is provided to illustrate a method which has been employed for producing non-roping steels of the present invention.

EXAMPLE I Ingot iron and nickel were melted in a laboratory type basic lined induction furnace under an argon atmosphere to minimize oxidation. One third of the total silicon and manganese addition was added to the molten bath for purposes of de-oxidation. Subsequently, a portion of the desired carbon and chromium was added in the form of low-carbon ferrochromium, after which an additional one-third of the silicon and managanese was added. This was followed by the addition of the remainder of the desired carbon and chromium in the form of high carbon ferrochromium, and by the addition of the remaining one-third of silicon and managanese.

The resulting molten bath was held at between 2830 F. and 2870 F. for 20 to 30 seconds for purposes of homogenization after which the molten material was tapped into ingot molds. The resulting ingots were cropped and hot-rolled to approximately /2 inch plate at between 2060 F. and 2100 F. The /2 inch plate was conditioned to remove physical defects and again hotrolled to about 0.165 inch at an initial temperature of 2000" F. The resulting plate was conditioned, annealed in an inert atmosphere for 1 hour at 1500 F., air cooled, pickled in 20 percent HNO +2 percent HP to remove scale, and cold-rolled to 0.05 inch sheet. The sheet thus obtained was in turn annealed in an inert atmosphere for 15 minutes at 1500 F., air cooled, pickled in 20 percent HNO +2 percent HP to remove scale, and finally coldrolled to 0.025 inch sheet.

In order to illustrate the advantages of the present invention, 0.025 inch chromium steel sheet having various chromium and carbon contents was manufactured in the manner described in the example. Sample blanks were cut from the produced sheet and degreased, annealed at 1400 F. and 1500 F. for 15 to 30 minutes, descaled (20 percent HNO +2 percent HF), and electrolytically polished in 75 percent H PO +25 percent H 80 The thus prepared specimens were then tested by being strained 20 percent in tension and examined for roping. The results of the tests appear in Table I.

Table I Composition, Percent Extent of Roping C Cr Mn Si Ni N 0. 036 12.14 0.35 None. 0. 071 12. 53 0. 50 0. 23 0.24 0. 022 D0. 0.076 "12. Do. 0.12 *12. 0 Do. 0. 014 "15. 0 Very Slight. 0.036 15. 16 D0. 0.060 *15. 0 0.36 None. 0.080 "15. 0 D0. 0.14 *15. 0 o Do. 0.084 16.5 0 Slight. 0.14 *16. None. 0.16 12.12 Do. 0. 026 17. 81 0. 67 0. 2G 0. 024 Severe. 0. 04 17.18 Slight. 0. 0G 17. 17 0.32 0. 36 0. 036 Severe. 0.08 17.41 0. 18 0.26 0.37 Slight. 0. 09 *17. 5 o o 0 Very slight. 0.12 17.5 C) None. 0.13 *17. 5 Do. 0. 08 19.16 Severe. 0. 027 20. 0 Very slight. 0.043 20. 57 Slight. 0. 054 20. 58 0. 67 0.39 0. 26 0. 020 Severe. 0. 07 20. 0 Very slight. 0. 09 20. 0 None. 0. 12 '20. 0 D0. 0.13 20. 0 Do. 0.17 20.12 C) Do. 0. 054 21. 39 0. 64 0. 39 0. 27 0. 029 Very slight. 0. 078 21.41 0. 63 0.41 0. 38 0. 023 None. 0. 12 21. 50 0. 66 0.42 0. 37 0. 022 Do. 0. 016 22. 0 Slight. 0. 044 22. 28 Severe. 0.062 22. G8 0. 67 0.41 0.32 0. 029 Slight. 0. 039 24. 13 Severe. 0. 064 24.48 0. 71 0.33 0. 30 0. 038 Slight. 0.076 24. 0 None. 0. 24. 07 0. 40 0. 026 Do. 0.11 "24.0 D0. 0.17 24. 0 D0. 0.10 26.02 D0. 0.15 *26. 0 0 Do.

Aim; aim is 0.60 pcrccnt manganese, 0.35 percent silicon, 0.25 percent nickel, 0.03 percent max. nitrogen, and as indicated for chromium.

To determine the further effect of the controlled chromium and carbon proportions in the steel of the present invention, tensile tests were performed on various samples and the results are set forth in Table H. It will be seen from Table II that the mechanical properties of the steel were not adversely affected by the increase of chromium and carbon, but were in fact somewhat improved.

Table II Percent Percent Yield Ult. Percent Cr Strength, Strength, Elongation p.s.i. p.s.i. in 2 inches It has further been found as a result of experimental testing that a very high level of corrosion resistance is achieved, in addition to the aforementioned advantages, with a steel in accordance with the present invention having a minimum carbon content of 0.095 percent and a chromium content between 16 and 19 percent.

It also has been found that steels of the present invention having a chromium content between 21 and 25 percent and a minimum carbon content of 0.07 percent are likewise characterized by a very high level of corrosion resistance.

From the foregoing it is evident that the present invention constitutes a substantial benefit to the art in providing a chromium steel which is uniformly deformable and which has the capability of being cold-formed without roping, in addition to other advantageous characteristics.

What is claimed is:

1. A non-roping, cold workable, uniformably deformable, ferritic chromium-bearing steel consisting essentially of from 21 to 25 percent chromium, a maximum of 1 percent manganese, 0.3 to 1 percent silicon, a maximum of 0.4 percent nickel, 0.022 to 0.04 percent nitrogen, and from 0.078 percentup to about 0.17 percent carbon, the actual carbon content for a selected chromium content being restricted to amounts to the right of the curve in the accompanying diagram, the balance being iron and incidental impurities.

2. In the manufactures of the class described, ropefree, cold-formed, chromium steel articles consisting essentially of from 21 to 25 percent chromium, a maximum of 1 percent manganese, a maximum of 1 percent silicon, 0.3 to 0.4 percent nickel, 0.02 to 0.04 percent nitrogen, and from 0.078 percent up to about 0.17 percent carbon, the actual carbon content for a selected chromium content being restricted to amounts to the right of the curve in the accompanying diagram, the balance being iron and incidental impurities.

References Cited by the Examiner FOREIGN PATENTS 259,920 11/ 1926 Great Britain. 563,249 8/1944 Great Britain.

OTHER REFERENCES American Society for Metals, preprint No. 23, 1950, page 8, edited by Binder et al.

Metals Handbook, 1939 edition, page 39, Alloy Bethadur 446.

5 AVID L. RECK, Primary Examiner. 

1. A NON-ROPING, COLD WORKABLE, UNIFORMABLY DEFORMABLE, FERRITIC CHROMIUM-BEARING STEEL CONSISTING ESSENTIALLY OF FROM 21 TO 25 PERCENT CHROMIUM, A MAXIMUM OF 1 PERCENT MANGENESE, 0.3 TO 1 PERCENT SILICON, A MAXIMUM OF 0.4 PERCENT NICKEL, 0.022 TO 0.04 PERCENT NITROGEN, AND FROM 0.078 PERCENT UP TO ABOUT 0.17 PERCENT CARBON, THE ACTUAL CARBON CONTENT FOR A SELECTED CHROMIUM CONTENT BEING RESTRICTED TO AMOUNTS TO THE RIGHT OF THE CURVE IN THE ACCOMPANYING DIAGRAM, THE BALANCE BEING IRON AND INCIDENTAL IMPURITIES. 